9,845 research outputs found
Different Power-law Indices in the Frequency Distributions of Flares with and without Coronal Mass Ejections
We investigated the frequency distributions of flares with and without
coronal mass ejections (CMEs) as a function of flare parameters (peak flux,
fluence, and duration of soft X-ray flares). We used CMEs observed by the Large
Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric
Observatory (SOHO) mission and soft X-ray flares (C3.2 and above) observed by
the GOES satellites during 1996 to 2005. We found that the distributions obey a
power-law of the form: dN/dX~X^-alpha, where X is a flare parameter and dN is
the number of events recorded within the interval [X, X+dX]. For the flares
with (without) CMEs, we obtained the power-law index alpha=1.98+-0.05
(alpha=2.52+-0.03) for the peak flux, alpha=1.79+-0.05 (alpha=2.47+-0.11) for
the fluence, and alpha=2.49+-0.11 (alpha=3.22+-0.15) for the duration. The
power-law indices for flares without CMEs are steeper than those for flares
with CMEs. The larger power-law index for flares without CMEs supports the
possibility that nanoflares contribute to coronal heating.Comment: 4 pages, 2 figures embedded, accepted for publication in ApJ
Breadth-first serialisation of trees and rational languages
We present here the notion of breadth-first signature and its relationship
with numeration system theory. It is the serialisation into an infinite word of
an ordered infinite tree of finite degree. We study which class of languages
corresponds to which class of words and,more specifically, using a known
construction from numeration system theory, we prove that the signature of
rational languages are substitutive sequences.Comment: 15 page
Discretized rotation has infinitely many periodic orbits
For a fixed k in (-2,2), the discretized rotation on Z^2 is defined by
(x,y)->(y,-[x+ky]). We prove that this dynamics has infinitely many periodic
orbits.Comment: Revised after referee reports, and added a quantitative statemen
The Physics of Wind-Fed Accretion
We provide a brief review of the physical processes behind the radiative
driving of the winds of OB stars and the Bondi-Hoyle-Lyttleton capture and
accretion of a fraction of the stellar wind by a compact object, typically a
neutron star, in detached high-mass X-ray binaries (HMXBs). In addition, we
describe a program to develop global models of the radiatively-driven
photoionized winds and accretion flows of HMXBs, with particular attention to
the prototypical system Vela X-1. The models combine XSTAR photoionization
calculations, HULLAC emission models appropriate to X-ray photoionized plasmas,
improved models of the radiative driving of photoionized winds, FLASH
time-dependent adaptive-mesh hydrodynamics calculations, and Monte Carlo
radiation transport. We present two- and three-dimensional maps of the density,
temperature, velocity, ionization parameter, and emissivity distributions of
representative X-ray emission lines, as well as synthetic global Monte Carlo
X-ray spectra. Such models help to better constrain the properties of the winds
of HMXBs, which bear on such fundamental questions as the long-term evolution
of these binaries and the chemical enrichment of the interstellar medium.Comment: 9 pages including 5 color encapsulated postscript figures; accepted
for inclusion in the proceedings of "Cool Discs, Hot Flows: The Varying Faces
of Accreting Compact Objects," ed. M. Axelsson (New York: AIP); minor
revision which addresses the referee's comments; added Fig. 1 and removed
Fig. 3 and the associated tex
The ground state of a spin-1/2 neutral particle with anomalous magnetic moment in a Aharonov-Casher configuration
We determine the (bound) ground state of a spin 1/2 chargless particle with
anomalous magnetic moment in certain Aharonov-Casher configurations. We recast
the description of the system in a supersymmetric form. Then the basic physical
requirements for unbroken supersymmetry are established. We comment on the
possibility of neutron trapping in these systems
Detection of high k turbulence using two dimensional phase contrast imaging on LHD
High k turbulence, up to 30 cm(-1), can be measured using the two dimensional COâ‚‚ laser phase contrast imaging system on LHD. Recent hardware improvements and experimental results are presented. Precise control over the lens positions in the detection system is necessary because of the short depth of focus for high k modes. Remote controllable motors to move optical elements were installed, which, combined with measurements of the response to ultrasound injection, allowed experimental verification and shot-to-shot adjustment of the object plane. Strong high k signals are observed within the first 100-200 ms after the initial electron cyclotron heating (ECH) breakdown, in agreement with gyrotron scattering. During later times in the discharge, the entire k spectrum shifts to lower values (although the total amplitude does not change significantly), and the weaker high k signals are obscured by leakage of low k components at low frequency, and detector noise, at high frequency
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